Method for production of compound iron powders



lViETHOD FOR PRODUCT'IGN OF COMPOUND. IRONIPGWDERS William.M. Shafer, .Johnstown,.l?a., assignor. to The Na tiOnaI-UJSLRadiatoI Company, a corporation 0"Mary-' land No Drawing. Application June 17, 1954, Serial N0;-437,569

7.' Claims. (Cl: 75*

ties,xfor. ins-tance't-o. improve the strength -or the. corrosion resistance of pressed and sintered parts. Certain difii- 1 cultiessand disadvantages attend that practice. For instance, there isalways the problem ofobtaining. .the necessary intimate mixture of the two metal powders and of. maintainingzitshomogeneityduring: handling and: in the pressing operations. Especially disadvantageous is the 1 elfect' producedfby some non-ferrous -.-metal powders, notably copper;,ofcausing an'undesirable' growth of parts sintered from mixtures of them withmost iron :powders. Such: increase in dimensions is objectionable in-that. it makes it ditficult .to produce accurately sizedparts;

It is among:the-objects ofthis invention to provide iron powders compounded with non-ferrous metals that-are easily and inexpensively produced; that avoid theforegoing disadvantages of the previous practiceof mixing powders of ironandncn-ferrous metals;-..thatproduce stronger pressed and sintered parts than: al'eto be obtainednby the ..-previous.practices; that. undergo little or no positive growth during sintering; .and which. maybe pressednand sinteredwithoutmodificationt-of existing practices in those operations;

Other objects will appear from the -following=specification;

The invention is predicated upon my -discoveryzthat the troubles and'z'disadvant-agesencounteredz in ther existing practice of mixing iron powder with a non-ferrous metal powder. :arezobviated i by :a compound ironpowder produced by heatingamixture-of: (-1) iron powder containinga substantial proportion ofcornbined carbon and (2) finely dividedoxide of a'metalthat is reducible by'carbon.

of non-homogeneity, thus avoiding the segregation that 5 tends to occur when simple mixtures of the two powders are used.

A major advantage of the compound powder made in accordance with this invention is that the growth, or increase in dimensions, that occurs with mixtures of most iron powders with copper is avoided, with, usually, an actual decrease in dimensions such as is desirable. Attendant also upon the use of these new compound iron powders is the advantageous fact that sintered strength is greater than with simple mechanical mixtures of the same composition.

The composition of the mixture of iron powder containing combined carbon and non-ferrous metal oxide will depend upon the content of non-ferrous metal desired 2,775,516 Patented Dec. 25,1056

amount'of' carbon 'desiredimthe final product. 1 Fonmany purposeszthe two" are mixed in proportions such that the iron powder will be decarburized, or atleast'have its carbon content reduced to a low value, say=11ot-more-thah about 012' percent; while effecting reduction of-all' of the non-ferrous meta-l oxide: However, for some purposes; as where steel parts susceptible to-hardening byheat treatment are desired; theresidual carbon in :the'co-mpoundpowdermaybeasdesired: In such-'instances and especially whererelatively large amounts ofnon-ferrous metal are to appear in, the compound powder, it is desirable that the starting iron-powder contain a high proportion of carbon as 'iron'carbide: -Ifonly small'amounts of.non:ferrous metal; oxide are to be reduced, desirably the combined carboncontent-of the iron-powder will be only such asto reducelthe oxideleavingthe-iron powder decarburized-or substantiallysor' In instances when it, is desired to keep the non-terrous metal contentilower than'it could-be 'keptif enough nonferrous metaloxid were added to sufliciently'decarburize the iron, sufiicienLdecarburization is achieved by; includ ing' an appropriateamount, of iron-oxide in the mixture. Mill scale .sufiices fior this purpose but-other iron oxides may beused'.

Inasmuch .as copper is thenon-fer rous metal most-commonlynsed with iron powder, the invention may be described in further-detail'with' reference to a compound iron-copper: powder: The carbon-containingiron powder is mixed with the appropriate-amount' of-finely divided cuprous or cupric oxide inproportions' that are approximately stoichiometric with respect to the total amount of carbon present and the'amountof oxide to be reduced. The iron powder and oxide are intimately mixed and then heated at 1600" t'o"-1900"F. in a closed container or in a furnace provided with a non-oxidizing'atmosphere that is inert. to'iron and'thelmetalof the'roxide. As exemplifying the benefits to be. derived from the; invention, reference may bemade to the following tests:

Powder -A.100-mesh'- ground. high carbon. iron, shot was decarburized with 100-meslimill scalepat 1650 F. in a protective atmosphere and then mixed with 11 percent bytweight of 10071116513. pure copper powder.

Powder B.I'l"-viz,entyt pounds of "1'00 mesh high carbon groundashot cont-aining 3107 percent of 'carbon' and 2.82 percenL-of'oxy-genwere mixed with 3.28p'ounds of copper :oxide1and2137'p'ounds of IOU-mesh mill scale. The .mixture was heated as with Powder A.

Powder C..A mixture of, by weight, 77.7 percent of ground 100-mesh iron shot containing 2.88 percent total 0 carbon and 1.46 percent of oxygen, 10 percent of 100-mesh in the compound powder, and also upon the content of combined carbon in the original iron powder and the mill scale, and 12.3 percent of IOO-mesh copper oxide was heated like Powders A and B.

Standard tensile bars were pressed at 30 tons per square inch using one percent of added zinc stearate as a lubri- 5 cant, and the bars were sintered in hydrogen for thirty It will be observed that there was substantial growth, both axially and radially in the case of the simple mechanical mixture of iron and copper powder. In marked contrast, in the case of Powders B and C produced in accordance with this invention there-was actual slight shrinkage in both directions with Powder B, axial shrinkage in the case of Powder C and only slight growth radially. The data show also the very substantial increase in strength of the bars pressed from Powders B and C as compared with those made from Powder A.

Although the invention has been described with particular reference to compound iron-copper powder, it is applicable also to other non-ferrous oxides, as evidenced by the following series of tests:

Powder D.-100-mesh annealed iron powder was mixed with 6 percent by weight of 325-mesh pure nickel powder.

Powder E.A mixture of, by weight, 81.28 percent of the ground high carbon shot used in producing Powder C, 9.36 percent of nickel oxide, and 9.36 percent of 100- mesh mill scale was heated at 1650 F. in a protective atmosphere.

Powder F.l-mesh annealed iron powder was mixed with one percent by weight of 325-mesh pure nickel powder.

Powder G.A mixture of, by weight, 81.3 percent of the iron powder used in making Powder C, 17.4 percent of 100-mesh mill scale, and 1.3 percent of nickel oxide was heated in the same manner used in producing Powder E.

Powders D to G were used for the production of tensile bars in the same manner as was done with Powders A to C. The composition of these powders and the test data are shown in the following table:

These data again show the shrinkage that characterizes the compound powders of this invention coupled with increase in strength as compared with articles made in the same way from mere mechanical mixtures of the same or closely similar composition.

Other oxides of non-ferrous metals may be used, if desired, for the development of special properties, examples being oxides of cadmium, lead, tin, bismuth, molybdenum and cobalt. Also, two or more such oxides may be present in the mixtures to be reduced.

According to. the provisions of the patent statutes, I have explained the principle of my invention and have described what I now consider to represent its bestem:

bodiment. However, I desire to have it understood that, within the scope of the appended claims, the invention may be practiced otherwise than as speoificially described.

Iclaim:

1. That method of making compound iron powder comprising mixing iron powder containing combined carbon with at least one finely divided oxide of a non-ferrous metal reducible by carbon, heating the mixture under nonoxidizing conditions to a temperature at which said oxide is reduced by the carbon of said powder, and recovering iron particles of lowered carbon content surface coated with the metal of said oxide.

2. A method according to claim 1, said oxide being selected from the group consisting of oxides of copper and nickel.

3. A method according to claim 2, said mixture also containing an iron oxide.

4. That method of making compound iron powder comprising mixing iron powder containing combined' carbon with at least one finely divided oxide of a non-ferrous metal reducible by carbon, the proportions of said powder and oxide being such as to provide carbon in an amount to reduce said oxide with production of iron powder of low carbon content, heating the mixture under non-oxidizing conditions to a temperature at which said oxide is reduced by the carbon of said powder, and recovering iron particles of lowered carbon content surface coated with the metal of said oxide.

5. A method according to claim 4, 881d mixture contaiuing also an iron oxide.

6. A method according to claim 5, said non-ferrous metal oxide being selected from the group consistingof oxides of copper and nickel. I

7. A method according to claim 4, said oxide being selected from the group consisting of oxides of copper and nickel, and said heating beingat 1600 to 1900 F.

References Cited'in the file of this patent UNITED STATES PATENTS 2,483,075 Truesdale Sept. 27, 1949 

4. THAT METHOD OF MAKING COMPOUND IRON POWDER COMPRISING MIXING IRON POWDER CONTAINING COMBINED CARBON WITH AT LEAST ONE FINELY DIVIDED OXIDE OF A NON-FERROUS METAL REDUCIBLE BY CARBON, THE PROPORTIONS OF SAID POWDER AND OXIDE BEING SUCH AS TO PROVIDE CARBON IN AN AMOUNT TO REDUCED SAID OXIDE WITH PRODUCTION OF IRON POWDER OF LOW CARBON CONTENT, HEATING THE MIXTURE UNDER NON-OXIDIZING CONDITIONS TO A TEMPERATURE AT WHICH SAID OXIDE IS REDUCED BY THE CARBON OF SAID POWDER, AND RECOVERING IRON PARTICLES OF LOWERED CARBON CONTENT SURFACE COATED WITH THE METAL OF SAID OXIDE. 